Method of rendering fabrics stretchable



y 2, 1967 G. w. MANOCK 3,316,610

METHOD OF RENDERING FABRICS STRETCHABLE Filed Dec. 2, 1963 2Sheets-Sheet 1 [NVf/V/Z/Z fia w M44016 42N006 y 2, 1967 G. w MANOCK3,316,610

METHOD OF RENDERING FABRICS STRETGHABLE Filed Dec. 2, 1963 2Sheets-Sheet 2 United States Patent 3,316,610 METHOD OF RENDERINGFABRICS STRETCHABLE Geoffrey Windle Manock, Han-agate, England, assignorto Imperial Chemical Industries Limited, London, England, a corporationof Great Britain Filed Dec. 2, 1963, Ser. No. 327,215 Claims priority,application Great Britain, Nov. 30, 1962, 45,345/ 62 Claims. (Cl. 2$-72)This invention relates to Woven fabrics having stretch characteristics.

Woven fabrics having stretch characteristics in the warp and or weft areknown. They may be produced by known methods comprising (i)Incorporating yarns containing fibres or filaments with elasticproperties during weaving such as rubber or stretchable elasticsynthetic polyurethane fibres or filaments.

(ii) Incorporating a yarn made from crimped filaments, examples areBan-lon a stuffer box crimped filament yarn, Helanca a twist crimpedfilament yarn and Crimplene a stabilised false twist crimped filamentyarn.

(iii) Subjecting a woven fabric to a treatment which results in yarncrimp and chemically setting this crimp.

We have found that with certain types of thermoplastic fibres, which maybe blended with natural or other manmade fibres, a chemical treatment isnot required if, instead, a major proportion of such suitablethermoplastic fibres are incorporated and this fabric is heated to fiXthe stretch properties.

According to my invention I provide a woven fabric which has stretchcharacteristics and which may be elongated by at least under a load of 2kg. on a 2 inch strip of the fabric in one direction i.e. either in thewarp or in the weft, due to yarn crimp which has been imparted by crimpinter-change and fixed by a heat treatment between two sets of yarns,the yarns with the yarn crimp comprising a proportion of syntheticthermoplastic fibres having a glass-rubber transition temperature whenwet, above 80 C.

The yarns of the first set having the yarn crimp, lie substantiallyparallel but with the crimps in neighbouring yarns out of phase witheach other, the yarns of said first set intertwining the yarns of thesecond set according to the weave pattern, the yarns of said second setlie in sub stantially parallel straight lines all in substantially oneplane, when the fabric is supported on a fiat planar surface.

The glass-rubber transition temperature of the synthetic thermoplasticfibres is determined by the dynamic extension method as described by P.R. Pinnock and I. M. Ward in Proc. Phys. Soc., vol. 81, part 2, No. 520,pages 260275, 1963. 1

Suitable synthetic thermoplastic fibres are polyester fibres derivedfrom terephthalic acid, particularly polyethylene terephthalate andother fibres derived from fibreforming polymers having a plastic memoryand a transition temperature when wet, above 80 C' The term fibresincludes staple fibres and filaments where the context so allows.

We also provide a process for imparting stretch characteristics to awoven fabric, comprising a proportion of synthetic thermoplastic fibreshaving a glass rubber transition temperature when wet, above 80 C.,which has substantially no long floats and is preferably of a plainweave construction and which may be dyed if desired, comprisingstretching the fabric in the direction of one set of parallel yarns,suitably by at least 5 to and as much as possible without breaking theyarns, whilst allowing the yarns in the other direction of the fabric torelax, suitably by at least 10 to 30%, to bring about yarn 3,3 lfifi WPatented May 2, 1967 crimp inter-change between the yarns in the twodirections of the woven fabric and heating the fabric for a time and ata temperature suitable for bringing about heat setting of the yarnswhich must comprise a proportion of the suitable synthetic thermoplasticfibres at least in the direction where no stretching has taken place andallowing the fabric to cool in that configuration before removing asubstantial proportion of the stretching force and so to maintain saidcrimp interchange.

By the term stretch characteristics we mean that the fabric can beelongated by at least 10% in at least one direction i.e. in the warp orweft direction and that this elongation under a load which must be belowthe elastic limit of the yarn crimp and not cause fibre rupture, isrecoverable by at least i.e. when releasing the stretching force, thefabric will rapidly assume substantially its previous size and shape. Aconvenient minimum load is 2 kg. on a 2 inch strip of the fabric.

It should be noted that although most fabrics can be stretched andrecovered from stretch the amount of stretch is only about 1 to 3%whereas our fabrics with the defined stretch characteristics can beelongated by at least 10%, preferably 15-30% after the treatment, butnot before.

We have found that quite simple operations in finishing can increaseyarn crimp and so give stretch characteristics. If warp stretch isrequired then warp crimp should be increased. This can be done bystretching the fabric in Width so that weft crimp is removed. Thiscauses the warp crimp to increase, by virtue of the crimp interchangeproperties of woven fabrics, and the correct amount of overfeed, thefabric will be reduced in length, as the wanp crimp develops.

The heat setting can conveniently be carried out during stentering andshould clearly be under conditions more severe than those likely to bemet during subsequent making-up or laundering treatments andtemperatures between and 220 C. preferably e.g. 180 C.200 C. for 30- 60secs. are considered adequate for our defined fibres. Under Wetconditions and in steam lower temperatures are adequate and temperaturesbetween the glass-rubber transition temperature and 30 C. below themelting point of the fibres may be used.

If weft stretch is needed, the fabric should be stretched in the warpdirection and allowed to relax in the weft direction, again the newfabric configuration being fixed by heat.

It has been found that the stretch characteristics vary with fabricconstruction and, for example, the effect is far greater in a looselywoven skirting than in a tightly woven rainwear fabric. If desiredfabric setts can be modified so that the required finished constructionis obtained.

If e.g. a pretreated fabric has little or no weft crimp, then we cannotstretch it in the weft direction and therefore, we cannot crimp theyarns in the warp to give warp stretch or vice versa.

Very firm fabrics, e.g. rainwear fabrics are diflicult to distort andtherefore difiicult to convert into our fabrics with stretchcharacteristics.

The yarns in the woven fabrics must be thermoplastic i.e. capable ofbeing heat set after crimp inter-change has taken place and thisdeformation of the crimped yarns must be elastic so that when a load isapplied of 2 kg. to a 2 inch strip of fabric, the fabric retracts againon removal of the load, due to the recovery from bending of the heat setyarns. It should be appreciated that the stretch properties of thefabric are due specifically to bending of the heat set yarns rather thanelongation of the individual filaments either by uncoiling of crimp oractual elastic elongation-as happens in known stretch fabrics composedof elongatable fibres such as rubber or of crimped filament yarns.

It will be apparent that in order to obtain the greatest elasticrecovery in bending, the yarns should be capable of being bent withoutseparation of the individual fibre or filament components. In otherwords yarns of substantially circular cross-section are preferred. Theyarns may be doubled or plied yarns but the individual yarns should havea circular cross-section; because of this, spun staple yarns arepreferred. If filament yarns are used they should be made to retaintheir substantially circular cross-section e.g. by twisting or by acoating.

After my treatment an examination of the heat set thermoplastic yarnsshow a sinusoidal crimp in one plane with a high birefringence of theoriented drawn filaments in the yarn and a high degree of crystallinitywhereas the yarns in the transverse direction are substantially straightparticularly if they also consist of thermoplastic yarns.

Natural and non-thermoplastic fibres can also be used in the transversedirection, if inferior stretch properties can be tolerated.

The condition for the heat fixation of the yarns in the fabric whentensioned in one direction will depend on the polymer from which thethermoplastic yarns are made. The temperature conditions must be chosendepending on the heat resistance of any fibres which may be blended withthe fibres responsible for the stretch characteristics and the weight ofthe fabric to allow suflicient heat penetration. The other considerationis that the treatment temperature should be in excess of that likely tobe encountered in subsequent processing, use and wear.

As already stated spun yarns are preferred to filament yarns forimparting the stretch properties to the fabric. For maximum stretchproperties the greatest possible amount of crimp interchange is requiredand this occurs with yarns which, as previously stated, maintain theircircular cross-section under transverse pressure against adjacent yarns.When filament yarns are used which have low twist, flattening occurswith resulting filament separation at the bends and as a result suchfabrics when subsequently stretched do not generate high yarn crimp bycrimp interchange because of filament interference.

For practical purposes the tensions required can be determinedsufficiently accurately by measuring the extension under loads which ofcourse must be less than those which would ruin the fabric by breakingindividual yarns. Extensions of -20% in one direction and allowing thefabric to relax in the transverse direction in which the thermoplasticheat settable yarns are by about 40%, are suitable for our fabrics.

Such fabrics after the treatment should have stretch characteristics ofat least 10% and may have 15-30% stretch in the warp or weft when testedunder a 2 kg. load for a 2 inch strip of fabric.

In order to obtain the required stretch in a fabric by our crimpinterchange method as a result of which the high sinusoidal yarn crimpis imparted by the transversely crossing threads, the plain weaveconstructions are preferred with approximately equal thread spacing bothin the warp and weft.

Fabrics having a cover factor of 13 have been found eminently suitablewhen woven from 67/33 Terylene/ Cotton blends.

The cover factor D denotes the number and denier or count of yarns inthe warp and weft of the fabric thus:

ends or picks per inch cotton count Lubrication of the yarns in thefabric is of importance. The tension required to produce a crimpinterchange is lower if inter-fibre and inter-yarn friction is low.Textile lubricants containing silicones are preferred.

The yarn crimp in the fabric increases with fabric sett and is at itshighest in a plain weave construction which therefore is preferred. Forexample a Terylene Cotton/Poplin rainwear fabric of a firm constructionwhich gives only 5% stretch after treatment i.e. stretching in onedirection and heat setting whilst relaxing in the other directiontransversely thereto, is unsuitable.

When crimp interchange takes place the slightly ondulating parallelyarns in one direction of the fabric are pulled substantially straight,and at the same time the parallel yarns in the other direction arethereby pulled closer together and the ondulating path over and underthe substantially straight yarns in the other direction is very muchenhanced. It will be appreciated that for this crimp interchange to bepossible the following requirements in fabric construction will have tobe met:

(a) The spacing between the yarns in both directions should be such thatthe yarns lie in an ondulating path due to inter-twining atsubstantially right angles to each other.

(b) The spacing between the yarns should be such as to allow movement ofthe yarns in the transverse diree= tion when the other set of yarns ispulled into straight lines under high tension.

(c) The spacing should not be too large between the yarns butappreciable ondulation should be present to cause a substantial movementof the yarns in the other direction when one set of yarns is pulled intostraights.

(d) To assist movement between the yarns a lubricant should be providedon the surface of the yarns. I

(e) During the heat treatment in the tensioned condition the ondulatedyarns should contain a major proportion of fibres or filaments which canbe heat set in that position under conditions such that this settingbecomes practically irreversible during any subsequent processing orduring wear.

Regarding (e) we have found that synthetic fibres hav; ing a glassrubber transition tempearture below C. do not show any particular meritwhen used in the fabrics of our invention because the imparted settingis not permanent and is removed by subsequent heat treatments attemperatures even below the setting temperature when wet. Such syntheticfilaments and fibres comprise the polyamides and isotacticpolypropylene. On the other hand polyester fibres derived fromterephthalic acid par ticularly polyethylene terephthalate fibres orcopolyester fibres containing up to 10% of a second component, as wellas polyacrylonitrile fibres and fibres containing at least 80%polyacrylonitrile are suitable since the stretch characteristicsimparted during our process are not sub: stantially affected bysubsequent heat treatment at least at tempeartures up to 80 C. i.e.below the glass-rubber transition temperature. No substantial distortionof the fabric during any subsequent heat treatment at tempera t-uresabove the treatment temperature should be allowed to take place.

From the foregoing it will be noted that the denier of the yarns willhave an effect on the amount of stretch which can be obtained in anyparticular fabric and that for the treatment to be effective our fabricswill have a characteristic appearance when examining the threads in thefabric preferably using a low degree of optical magnification. The yarnsor threads in one direction will be substantially straight and show acrimp elongation or ondulation of less than 3% under a load of 0.5g.p.d. whereas the yarns which are causing the stretch characteristicsin the fabric will show a crimp elongation of at least 15% and up to 50%under the same load. The ondulations which are illustrated in thedrawing, take a substantially sinusoidal path, the angle of straightlines between the apices of the ondulations or crimps are preferablyless than of angle.

If our process is carried out on a continuous and commercial scale on apin stenter and it is desired to impart e.g. warp stretchcharacteristics to the fabric, the stenter is adjusted to give a highweft tension and overfeed is increased until waviness along the selvedgeof the suitable fabric is noticed. The overfeed is then reduced untilthe waviness just disappears. In a suitable fabric, crimp interchangewill take place, provided the weft tension is sufiicient i.e. that theweft yarns come to lie in a single plane in substantially parallelstraight lines, whereas before this weft tensioning, the weft yarns layin ondulating substantially parallel path.

It is also possible, instead, to impart weft stretch to the fabric byapplying warp tension and weft relaxation. If a pin or clip stenter isused the fabric should be stretched to the full desired extent before itis pinned or clipped. If this is not done the pins or clips will preventwarp extension. It is desirable to increase the grip of the deliveryrollers.

When the desired tension has been applied to bring about the crimpinterchange, the fabric is heat set in that condition and cooled, beforeallowing any relaxation.

Instead of a stenter, cylinder setting machines can be used in which thefabric is held on cylinders rotating at progressively faster speeds,while it is pressed e.g. by pressure belts against the cylinders. Suchmachines are commercially available. One type is known as the BatesCylinder Machine; it requires some modifications, by including theprovision of tensioning bars at the feed end. In this case setting.occurs on the cylinders which are heated to an appropriate temperaturein order to bring about heating of the fabric to a temperaturethroughout of up to 200 C., preferably 180 C., depending on a givenspeed and heat transfer properties of the fabric.

In the case of fibres which have a rubber transition temperature whenwet above 80 C., such as polyethylene terephthalate fibres I havesurprisingly found that fabrics containing a major proportion of suchfibres can be heat set e.g. to a first temperature as high as up to 30C. below the melting point of the fibre, followed by my treatment at alower second temperature, i.e. above the glass rubber transitiontemperature and at least 60 C. below the melting point, cooled to roomtemperature and then if desired heated a third time at a temperaturelower than the second temperature but without applying any overalltensions in the stretch direction of the fabric, treated according toour invention.

This is of considerable practical importance since such a woven fabriccan be heat set and stabilised against creasing at say 180 C., thentreated according to our invention including heating for a second timeat say 180 C. for 30 secs, to impart stretch properties to the fabricand cooling to below the glass rubber transition temperature, and whenmade up in garment form e.g. trousers, a pleat may be inserted e.g. on aHoffman press at say 135 C. for 1 minute without overall distortion ofthe fabric, thus resulting in a garment with a durable pleat, stretchcharacteristics in one direction and stabilised against shrinkage.

I, therefore, also provide a process for imparting stretchcharacteristics in one direction to a woven fabric made from polyesterfibres at least in the direction in which it is desired to impartstretch characteristics comprising heat setting the fabric at atemperature 30 C. above the glass rubber transition temperature and atleast 30 C. below the melting temperature of the polyester, stretchingthe fabric in one direction and allowing the fabric to relax in theother direction and which must contain a major proportion of polyesterfibres or filaments to bring about crimp interchange and so that theyarns in the direction of tensioning come to lie substantially in asingle plane along substantially straight parallel lines, heating thefabric in that condition at a temperature above the glass rubbertemperature and 30 C. below the melt temperature, cooling the fabric inthat condition and if desired subjecting the fabric to a subsequentthird heating at a temperature above the rubber transition temperatureand if desired below the said second temperature without, however,applying any overall distortion to the fabric for the purpose of, forexample, ironing or pleating but excluding stretching in the directionin which stretch characteristics have been imparted to the fabric.

The proportion of synthetic thermoplastic fibres required will depend ona number of disconnected factors such as fabric and yarn constructionand the end-use for which the fabric is required; a proportion of 35% inblends with wool may be used but higher proportions i.e. a majorproportion and including of the synthetic fibres have given excellentresults.

The attached drawings illustrate a preferred embodiment of our inventionin which FIGURE 1 is a diagrammatic isometric view of an untreatedfabric on a greatly enlarged scale.

FIGURE 2 is an isometric diagrammatic view of the fabric of FIGURE 1 asit appears during or after the heat treatment.

FIGURE 3 is a sectional end view of the fabric of FIG URE 1.

FIGURE 4 is a sectional end view of the fabric of FIGURE 2.

FIGURE 5 is a diagrammatic side view of a cylinder setting machine, on amuch reduced scale.

Referring to FIGURE 1 it will be seen that the yarns 1, 2 and 3 areinterwoven with yarns 5, 6, 7 and 8. It will be seen that the yarns 1, 2and 3 are slightly displaced through interaction with the yarn 5 (in thewarp) and as can be seen by reference to FIGURE 3, where an additionalyarn 4 is shown. When such a fabric is overfed onto a stenter in thewarp direction and then stretched in the weft direction the weft yarnsare straightened along virtually straight lines as can be seen byreference to FIG- URE 2, whereas the yarns in the warp direction are displaced by crimp interchange, the ondulations having been taken out fromthe weft yarns and increased in the Warp direction in the yarns 5, 6, 7,8 and 9. FIGURE 4 which is a section through the fabric of FIGURE 2along yarn 5 illustrates more clearly the greater crimp imparted to theyarn 5 and also that the yarns 1, 2, 3 and 4 in the warp direction nowlie virtually in one plane.

Referring to FIGURE 5 a suitably woven fabric is unwound from a clothbeam 10 and taken over an adjustable tensioning device comprisingquadrangular beams 11, 12, 13, 14 and 15, in which the two beams 12 and13 can be pivoted around axis 16 by a hand wheel 17. From beam 15 thecloth is taken up by feed rolls 18 and 19 followed by expander roll 20for spreading the cloth before it is taken up by the heated cylinders 21and 22, against which the cloth is pressed under higher pressure fromdriven transport rolls 23 and 24. Additional rolls 25, 26, 27 and 28 arecovered with two sets of aprons 29 and 30 which help to press the clothagainst the cylinders 21 and 22. Delivery roll 31 feeds the cloth into acooling zone 33 where the fabric may be suitably cooled with a blowerusing air at ambient temperature, before it is taken up by winding roll32 to be wound up as cloth roll 34 The following examples illustrate butdo not limit our invention.

Example 1 A 100% Terylene 1 plain weave fabric, made from 2/30s (cottoncount) yarn was stretched 10% in the weft direction and allowed to relax15% in the warp direction, the fabric being heat fixed at 200 C. for 30secs.

The treatment gave over 12% warp stretch which was Registered trademark,a polyethylene terephthalate fibre 711515 a )g1ass-rubber transitiontemperature when wet of durable to washing and which had good recoveryproperties.

Example 2 A 67/33 Terylene cotton fabric woven plain from 1/12s (cc.)was stentered at 180 C. for 30 secs. with 20% overfeed and 15% Weftstretch. The treatment gave 15% warp stretch again with good recoveryand durability to washing.

Settl Percent Yarn Crimp Initial 56 x 40 warp x 7% welt. After treatment48 x 50 18% warp x 2% \veit. Stretch at 2 kg./2 inch st Recovery fromstretch... 97%.

Example 3 A 67/33 Terylene/viscose, 1/l6s cotton count plain weavefabric having a cover factor of 13.2 was treated on a stenter at 180 C.for 30 seconds giving it a warp extension of 8% and allowing weftcontraction of 28%, as indicated in the following table which alsoincludes the properties of the fabric before and after the treatment.

Treatment Before After Sett (threads per inch) 56 x 50 72 x 46 Percentyarn crimp 8 x 7 1 x 30 Percent stretch at 2 kg./2 in. strip. 26 Percentrecovery from stretch 98 Warp extension 8%; Weft contraction 28%.

Example 4 Example 5 A 55/45 Terylene wool worsted plain weave 11Registered trademark, e. polyethylene terephthalate fibre \vigh acglass-rubber transition temperature when wet of t 0 8 oz./58" widthsuiting fabric, with x 60 threads per inch was treated as in Example 4.After the treatment the fabric had 14% stretch; x 58 threads per inch.On repeated stretching and release from a 2 kg. load on a 2 inch stripof fabric, 98% of the 14% stretch remained in the weft of the fabric.

What I claim is:

1. A process for imparting stretch characteristics to a fabric wovenfrom two sets of parallel yarns, one of said sets including yarnscomprising a proportion of synthetic thermoplastic fibres having aglass-rubber transition temperature when wet, above C., said processcomprising: stretching the fabric in the direction of the other set ofyarns to remove ondulations therefrom, as much as possible withoutbreaking the yarns, while allowing the yarns in said one set to relaxthereby to increase the yarn crimp therein and thereby establishingcrimp interchange between the two sets of yarns; heat-setting theincreased crimp in the yarns in said one set; and cooling the fabric tobelow the rubber transition temperature of the fibres in said one setbefore removing a substantial proportion of the stretching force so asto maintain said crimp interchange.

2. A process according to claim 1 comprising stretching the fabric inthe direction of said other set of parallel yarns by at least 5 to 15%.

3. A process according to claim 1 comprising allowing the yarns in saidone set to relax by at least 10 to 30% to bring about yarn crimpinterchange.

4. A process according to claim 1 in which setting is carried out duringstentering at temperatures between and 220 C.

5. A process according to claim 1 in which setting is carried out on acylinder setting machine provided with tensioning bars at the feed end.

References Cited by the Examiner UNITED STATES PATENTS l/l934 Cluett26--l8.6 2/1958 Skeer 2872

1. A PROCESS FOR IMPARTING STRETCH CHARACTERISTICS TO A FABRIC WOVENFROM TWO SETS OF PARALLEL YARNS, ONE OF SAID SETS INCLUDING YARNSCOMPRISING A PROPORTION OF SYNTHETIC THERMOPLASTIC FIBRES HAVING AGLASS-RUBBER TRANSITION TEMPERATURE WHEN WET, ABOVE 80* C., SAID PROCESSCOMPRISING: STRETCHING THE FABRIC IN THE DIRECTION OF THE OTHER SET OFYARNS TO REMOVE ONDULATIONS THEREFROM, AS MUCH AS POSSIBLE WITHOUTBREAKING THE YARNS, WHILE ALLOWING THE YARNS IN SAID ONE SET TO TELAXTHEREBY TO INCREASE THE YARN CRIMP THERIN AND THERBY ESTABLISHING CRIMPINTERCHANGE BETWEEN THE TWO SETS OF YARNS; HEAT-SETTING THE INCREASEDCRIMP IN THE YARNS IN SAID ONE SET; AND COOLING THE FABRIC TO BELOW THERUBBER TRANSITION TEMPERATURE OF THE FIBRES IN SAID ONE SET BEFOREREMOVING A SUBSTANTIAL PROPORTION OF THE STRETCHING FORCE SO AS TOMAINTAIN SAID CRIMP INTERCHANGE.